Low-energy Collimator Research Articles

РАЗРАБОТКА ПРОГРАММНЫХ СРЕДСТВ МАТЕМАТИЧЕСКОГО ИМИТАЦИОННОГО МОДЕЛИРОВАНИЯ НА ОСНОВЕ КЛИНИЧЕСКИХ ДАННЫХ И ФАНТОМНЫХ ИССЛЕДОВАНИЙ ДЛЯ ОЦЕНКИ ПЕРФУЗИИ ГОЛОВНОГО МОЗГА И ПОВЫШЕНИЯ КАЧЕСТВА ИЗОБРАЖЕНИЙ ПРИ ОФЭКТ/КТ С 99MTC-ГМПАО

Purpose: To develop a software package Virtual examination of brain perfusion by the method of SPECT/CT with 99mTc-HMPAO (Teoxime) and its practical application to study the conditions for achieving the best image quality in clinical studies of patients. Material and methods: The studies were performed using clinical data and the method of computer simulation. Clinical data of single-photon emission computed tomography combined with X-ray computed tomography (SPECT/CT) with 99mTc-hexamethylpropyleneamine oxime (99mTc-Teoxime, produced by DIAMED LLC) of a patient with an ischemic stroke of the right frontal cortex were obtained on a two-detector gamma-camera NM/CT 670 DR GE Discovery (USA) using high-resolution low-energy collimators (LEHR). The measured data were processed using specialized software Q.Brain and Q.Volumetrix MI on a Xeleris 4.0 DR workstation from GE Healthcare (USA) to obtain reconstructed axial tomographic slices. To carry out simulation computer simulation of the procedure of examination of perfusion of GM by the method of SPECT/CT has developed a software package that includes a mathematical Hoffman phantom with the ability to simulate clinical cases of hypoperfusion of different localization and size (Virtual Patient), modeling the collection of “raw” projection data and an image reconstruction program based on the OSEM algorithm (Ordered Subset Expectation Maximization). An important advantage of the mathematical modeling method is the ability to assess the quality of the reconstructed image by calculating the root-mean-square error when compared with a given phantom. In numerical experiments, the dependence of the reconstruction error on the parameters of the OSEM algorithm (on the number of subgroups – subsets, and on the number of iterations) was investigated in order to determine the conditions for achieving the best image quality. A statistical stop criterion was developed and tested. Results: For the first time, a software package was developed and tested that allows us to investigate errors in the reconstruction algorithm, which is a great difficulty when using clinical research methods. A criterion for stopping iterations is proposed when using the OSEM reconstruction algorithm – minimizing the functional deviation of the chi-square function from the target value, while the detector pixels with non-zero values are combined into blocks according to the 2×2 scheme. There is a reliable good correlation between the proposed stop criterion and the minimum of the root-mean-square error of image reconstruction. This makes it possible to introduce this criterion into the clinical practice of using computational tools for reconstructing sections of the SPECT to obtain the best image. The simulation results demonstrated the possibility of reducing the time of data recording, during which the patient must remain motionless, at least twice. Conclusion: The method of computer simulation developed in this work is a practically useful technology that helps optimize the use of SPECT to achieve the best possible results of brain imaging in patients.

Monte Carlo simulation study to explore optimum conditions for Astatine-211 SPECT.

211At is a promising nuclide for targeted radioisotope therapy. Direct imaging of this nuclide is important for in vivo evaluation of its distribution. We investigated suitable conditions for single-photon emission computed tomography (SPECT) imaging of 211At and assessed their feasibility using a homemade Monte Carlo simulation code, MCEP-SPECT. Radioactivity concentrations of 5, 10, or 20kBq/mL were distributed in six spheres in a National Electrical Manufactures Association (NEMA) body phantom with a background of 1kBq/mL. The energy window, projection number, and acquisition time were 71-88keV, 60, and 60s, respectively, per projection. A medium-energy collimator and three low-energy collimators were tested. SPECT images were reconstructed using the ordered subset expectation maximization (OSEM) method with attenuation correction (Chang method) and scatter correction (triple-energy-windows method). Image quality was evaluated using the contrast-to-noise ratio (CNR) for detectability and the contrast recovery coefficient (CRC) for quantitavity. The low-energy, high-sensitivity collimator exhibited the best detectability among the four types of collimators, with a maximum CNR value of 43. In contrast, the low-energy, high-resolution collimator exhibited excellent quantitavity, with a maximum CRC value of 102%. Scatter correction improved the image quality. In particular, the CRC value almost doubled after scatter correction. The detection of spheres smaller than 20mm in diameter was difficult. In summary, low-energy collimators were suitable for the SPECT imaging of 211At. In addition, scatter correction was extremely effective in improving the image quality. The feasibility of 211At SPECT was demonstrated for lesions larger than 20mm.

SPECT findings on neuropsychiatric symptoms caused by nitrous oxide abuse.

The aim of the study was to investigate the clinical, neuropsychological, and regional cerebral blood flow (rCBF) perfusion changes in patients with neuropsychiatric symptoms caused by nitrous oxide (N2O) abuse. A total of 16 patients with neuropsychiatric symptoms caused by nitrous oxide abuse were recruited for this study. The study was carried out in the withdrawal phase of N2O abuse. A 925-1110 MBq 99mTc-ECD was administered intravenously. SPECT/CT images were collected with a low-energy and high-resolution collimator. The region uptake statistics of different brain regions of interest between patients with N2O abuse and normal people of the databases for younger subjects from the Scenium DB Comparison software were calculated automatically. The clinical manifestations of the 16 patients with neuropsychiatric symptoms were mood lability, anxiety, hallucination, delusion, agitation, confusion, and other psychiatric symptoms. In addition, 15 of the patients also complained of memory decline; 14 patients manifested numbness or paresthesia; 14 patients developed limb weakness, and their motor impairments were more severe in the lower limbs than in the upper limbs; and eight patients had urinary and defecation disturbances. In the neuropsychological examination, the BPRS score was 54.69 ± 11.48, the HAMD score was 30.00 ± 11.06, the HAMA score was 18.06 ± 5.77, the MMSE score was 28.06 ± 2.29, and the MoCA score was 25.06 ± 3.40. SPECT showed hypoperfusion in the frontal and temporal lobes, which is consistent with the clinical findings. This was the first study to demonstrate the obvious effect of N2O abuse on CBF in patients with neuropsychiatric symptoms. CBF perfusion imaging is helpful to detect the changes in the local brain functional activity in patients with N2O abuse.

Study of the diagnostic efficiency of single-photon emission computed tomography with [<sup>99m</sup>Tc]Tc-1-THIO-D-glucose in visualization of brain tumors

The aim of the study was to evaluate the feasibility of using single-photon emission computed tomography (SPECT) with [99mTc]Tc-1-THIO-D-glucose in the detection of brain tumor malignancy. Material and methods. The study included 70 patients diagnosed with grade II–Iv malignant brain tumors and 10 patients with benign brain tumors. The control group consisted of 20 patients who had no pathological changes in the brain at the time of diagnosis. All patients underwent single-photon emission computed tomography of the brain 40 minutes after intravenous injection of [99mTc]Tc-1-THIO-D-glucose at a dose of 500 MBq. The [[99mTc]Tc-1-THIO-D-glucose radiopharmaceutical was prepared directly in the nuclear medicine department in strict accordance with the instructions. The head and neck of the patient fell into the field of view of the detectors of the gamma camera, 32 projections were recorded in a matrix of 256×256 pixels without hardware magnification. High-resolution low-energy collimators were used. Results. In patients with verified diagnosis of malignant brain tumors, SPECT with [99mTc]Tc-1-THIO-D-glucose correctly visualized tumors in all cases. The tumor was visualized as a zone of increased accumulation of [99mTc]Tc-1-THIO-D-glucose of varying intensity and size. However, benign brain lesions did not show [99mTc]Tc-1-THIO-D-glucose uptake. Physiological accumulation of [99mTc]Tc-1-THIO-D-glucose was observed in soft tissues of the aponeurotic helmet, the choroid of the brain, the mucous membranes of the nasal cavity, and the sinuses of the skull bones. Pathological changes in the brain revealed by SPECT were confirmed by MRI with contrast enhancement. Conclusion. The study demonstrated a high efficiency of SPECT with [99mTc]Tc-1-THIO-D-glucose in visualization of malignant brain tumors. The sensitivity, specificity and accuracy of SPECT with [99mTc]Tc-1-THIO-D-glucose in the imaging of malignant brain tumors were 93–100 %, 65–100 %, 95–100 %, respectively. The data obtained suggest that [99mTc]Tc-1-THIO-D-glucose SPECT as an additional method for the detection of malignant brain tumors can increase access to radionuclides for this group of patients and improve the quality of cancer care.

Initial clinical experience with dedicated multi-pinhole (MPH) collimator for 99mTc-HMPAO brain perfusion SPECT.

Dedicated multi-pinhole (MPH) collimators have been successfully tested in selected clinical investigations. The aim of our work was to report initial experiences with an MPH collimator set designed for brain perfusion single photon emission tomography (SPECT). Ten patients underwent sequential technetium-99m-hexamethylpropyleneamineoxime (99mTc-HMPAO) SPECT with a dual-head SPECT camera equipped with conventional low-energy parallel hole collimators (LEHR), and with a triple-head system equipped with MPH collimators. Low-energy parallel hole collimators data were reconstructed by filtered back projection (FBP), ordered subset expectation maximization (OSEM), software for tomographic image reconstruction (STIR). In addition, both the parallel hole data and MPH data were reconstructed by Tera-TomoTM 3D iterative reconstruction denoted LEHR_TT3D and MPH_TT3D, respectively. Five medical experts visually compared the reconstructed images of the five data sets and defined a ranking sequence from the lowest (1) to the highest (5) image quality. Results were compared using the Friedman test. P values below 0.05 were considered significant. Low-energy parallel hole collimators acquisition resulted in 5 million, while MPH acquisition in 13 million total counts with 30 and 34 minutes of acquisition time, respectively. Mean rank coefficients of the reconstruction methods were 1.96±0.52, 2.66±0.46, 2.86±0.60, 3.62±0.55, 3.9±0.68 for FBP, STIR, LEHR_TT3D, LEHR_OSEM, MPH_TT3D respectively. The differences between MPH_TT3D-FBP (P<0.01); MPH_TT3D-STIR (P<0.05); LEHR_OSEM-FBP (P<0.01) were significant. Image quality provided by MPH collimator is comparable to that provided by conventional LEHR imaging. Higher sensitivity has the potential to shorten acquisition time or to reduce the amount of administered activity.

Comparison of Low-Energy and Medium-Energy Collimators for Thyroid Scintigraphy with123I

CE credit: For CE credit, you can access the test for this article, as well as additional JNMT CE tests, online at https://www.snmmilearningcenter.org Complete the test online no later than March 2025. Your online test will be scored immediately. You may make 3 attempts to pass the test and must answer 75% of the questions correctly to receive Continuing Education Hour (CEH) credit. Credit amounts can be found in the SNMMI Learning Center Activity. SNMMI members will have their CEH credit added to their VOICE transcript automatically; nonmembers will be able to print out a CE certificate upon successfully completing the test. The online test is free to SNMMI members; nonmembers must pay $15.00 by credit card when logging onto the website to take the test.123I thyroid scintigraphy can be performed with either a low-energy or a medium-energy (ME) collimator. The high-energy photon emissions from 123I cause septal penetration with scattered photons, which deteriorate image quality. The aim of this study was to evaluate the impact of collimator choice on 123I thyroid scintigraphy in clinical practice. Methods: Forty-seven patients who underwent thyroid planar scintigraphy with both a low-energy, high-resolution (LEHR) collimator and a ME collimator were prospectively recruited using the same imaging protocol. Image quality, collimator sensitivity, and estimation of thyroid size were assessed between LEHR and ME collimators and were compared with thyroid ultrasonography as the gold standard. Results: Images acquired with the ME collimator demonstrated reduced scattered background noise, improved thyroid-to-background contrast, and increased sensitivity in the thyroid gland compared with images acquired by the LEHR collimator. Manual measurement of the thyroid length is more accurate using the ME collimator. Automatic estimation of the thyroid area using the same thyroid threshold is larger in ME collimator images than in LEHR collimator images. Conclusion: Compared with the LEHR collimator, the ME collimator generates cleaner 123I thyroid scintigraphy images with less background noise and has higher collimator sensitivity for thyroid imaging. Different thyroid thresholds should be used to estimate the thyroid area and volume between low and ME collimators.

Comparison of low energy and medium energy collimators in the quantitative assessment of 123I-MIBG cardiac sympathetic innervation imaging

Abstract Funding Acknowledgements Type of funding sources: Public hospital(s). Main funding source(s): University Clinic Hospital of Valencia Aim The assessment of cardiac sympathetic innervation by 123I-metayodobenzylguanidine (123I-MIBG) has proved useful in patients with heart failure and neurodegenerative disorders. The standard quantification of global cardiac uptake is to obtain the heart to mediastinum (HM) ratio in planar images, while SPECT images provide better evaluation of regional extent of denervated areas. Although low energy (LE) collimator has been widely used in these patients, septal penetration of high-energy photons of 123I could affect image quality and quantification accuracy. We have compared in the same patients the effect of collimator type on image quality and quantitative assessment of HM ratio. Methods In a group of 14 patients (11 men, 57-77 y/o, 66.4 ± 5.6) submitted for cardiac sympathetic study, we obtained successive planar anterior chest images 4h after the IV administration of 10 mCi of 123I-MIBG with a low-energy-high-resolution (LEHR) and a medium-energy (ME) collimators. Images were obtained with the same gammacamera Brightview Philips for 10 min on 256x256 matrix, with 159 Kev photopeak and unchanged patient position. For quantification of HM ratio, we use in each patient the same manual heart ROI and rectangular upper mediastinum ROI in the two acquired images to obtain the corresponding HM ratio. Results The image quality was better in all the patients with ME collimator acquisition than with LEHR collimator acquisition, and the HM ratio showed higher values with ME: 1.65-2.61 (mean 2.15 ± 0.28) than with LEHR: 1.27-1.85 (mean: 1.51 ± 0.18) with a mean difference of 0.64 ± 0.15 (0.38-0.88) between ME and LEHR and a mean ratio LEHR/ME of 0.70 ± 0.04 (0.64-0.79). In 9 patients with HM ratio ≤ 1.60 obtained from LEHR collimator acquisition, the mean difference with HM ratio obtained with ME collimator was 0.61 ± 0.12 and mean ratio LEHR/ME was 0.69 ± 0.03 and in 5 patients with HM ratio(LEHR) &amp;gt;1.60, mean difference with HM ratio(ME) was 0.69 ± 0.19 and mean ratio LEHR/ME was 0.71 ± 0.02. Conclusion Use of a ME collimator provides better image quality than LEHR collimator in planar images and higher values of HM ratio, providing a more accurate quantification of cardiac uptake in the patients submitted for evaluation of cardiac sympathetic innervation by 123I-MIBG, and could also improve the evaluation of regional impairment and extent of denervated areas by SPECT.

Interobserver Agreement in the Diagnosis of Parkinson Disease with Cardiac 123I-Metaiodobenzylguanidine Scintigraphy.

The aim of this study was to analyze the interobserver agreement of visual and quantitative assessment of cardiac 123I-metaiodobenzylguanidine scintigraphy. Methods: Planar images were acquired using a low-energy collimator. The heart-to-mediastinum (HM) ratio was adjusted for the use of a low-energy collimator, using a published formula. Interpretation was undertaken both visually and after the addition of adjusted HM ratios. Image findings were classified as normal, abnormal, or borderline. Results: The cohort consisted of 10 patients. On visual interpretation only, there was strong agreement on the interpretation of the scan (κ = 0.82, P < 0.01). Adjusted HM ratios led to a significant increase in mean ratios (1.79 vs. 1.36, P = 0.02) and, when utilized in reporting, resulted in perfect agreement (κ = 1.0, P < 0.01). Conclusion: The use of quantified HM ratios adjusted for low-energy collimator use improves on visual assessment alone and allowed for excellent interobserver agreement.

Abdominal obesity, and not general obesity, is associated with a lower 123I MIBG heart-to-mediastinum ratio in heart failure patients with preserved ejection fraction.

The relationship between general obesity or abdominal obesity (abdominal circumference of ≥85cm in men and ≥ 90cm in women) and the heart-to-mediastinum ratio (HMR), a measure of cardiac sympathetic innervation, on cardiac iodine-123-metaiodobenzylguanidine scintigraphy (MIBG) in patients with heart failure with preserved ejection fraction (HFpEF) has not been clarified. A total of 239 HFpEF patients with both MIBG and abdominal circumference data were examined. We divided these patients into those with abdominal obesity and those without it. In the cardiac MIBG study, early phase image was acquired 15-20min after injection, and late phase image was acquired 3h after the early phase. A HMR obtained from a low-energy type collimator was converted to that obtained by a medium-energy type collimator. Early and late HMRs were significantly lower in those with abdominal obesity, although washout rates were not significantly different. The incidence of patients with early and late HMRs <2.2 was significantly higher in those with abdominal obesity. Multivariate linear regression analysis revealed that abdominal obesity was independently associated with early HMR (standardized β = -0.253, P = 0.003) and late HMR (standardized β = -0.222, P = 0.010). Multivariate logistic regression analysis revealed that abdominal obesity was independently associated with early (odds ratio [OR] [95% confidence interval {CI}] = 4.25 [2.13, 8.47], P < 0.001) and late HMR < 2.2 (OR [95% CI] = 2.06 [1.11, 3.83], P = 0.022). Elevated BMI was not significantly associated with low early and late HMR. The presence of abdominal obesity was significantly associated with low early and late HMR even in patients without elevated BMI values. Abdominal obesity, but not general obesity, in HFpEF patients was independently associated with low HMR, suggesting that visceral fat may contribute to decreased cardiac sympathetic activity in patients with HFpEF. UMIN000021831.

Super Spatial Resolution (SSR) method for small animal SPECT imaging: A Monte Carlo study

This work used Monte Carlo (MC) simulations in order to investigate the feasibility of the application of a super-resolution method, namely Super Spatial Resolution (SSR), to a preclinical SPECT system. The SSR method is used to obtain a resolution enhancement by combining several images containing slightly different perspectives of the same scene.MC simulations are a useful tool in the development of new imaging devices, as well as in the assessment of new reconstruction methods. In this respect, GATE (Geant4 Application for Emission Tomography) is an open source platform dedicated to numerical MC simulations that has become a well validated toolkit for the simulation of SPECT and PET systems.We modelled a four-headed preclinical SPECT scanner capable of the proper movements in order to obtain the SSR acquisition sequences. Each detector is based on a CsI(Tl) pixelated scintillator coupled to a low-energy tungsten collimator with parallel square holes.Several phantoms and radioactive sources were simulated, in order to assess the performance of the proposed SPECT scanner. In addition, a complex voxelized phantom of a mouse was used to obtain realistic images with the aim of evaluating the system as a suitable tool for small animal imaging.The whole system sensitivity was 164.1 cps/MBq. In order to assess the impact of the SSR this value must be divided by the number of the images acquired to perform this method. The average value of the trans-axial resolution improves from 2.4 mm to 1.54 mm, 1.21 mm and 1.03 mm by respectively applying the SSR based on two, three or four images. While the average axial resolution changes from 1.69 mm to 1.49 mm, 1.15 mm and 0.98 mm by respectively using the SSR based on two, three or four images. The mouse images obtained by using the voxel phantom have demonstrated the good capability of the system as a suitable tool for small animal imaging.Finally, a comparison with commercial preclinical scanners has proved that the presented SSR scanner provides an alternative to pinhole SPECT systems for many preclinical research studies.

Digital Solid-State SPECT/CT Quantitation of Absolute 177Lu Radiotracer Concentration: In Vivo and In Vitro Validation.

The accuracy of 177Lu radiotracer concentration measurements using quantitative clinical software was determined by comparing in vivo results for a digital solid-state cadmium-zinc-telluride SPECT/CT system with in vitro sampling. Methods: First, image acquisition parameters were assessed for an International Electrotechnical Commission body phantom emulating clinical count rates loaded with a lung insert and 6 hot spheres with a 12:1 target-to-background ratio of 177Lu solution. Then, the data of 28 whole-body SPECT/CT scans of 7 patients who underwent 177Lu prostate-specific membrane antigen radioligand therapy were retrospectively analyzed. Three users analyzed SPECT/CT images for in vivo urinary bladder radiotracer uptake using quantitative software. In vitro radiopharmaceutical concentrations were calculated using urine sampling obtained immediately after each scan, scaled to SUVs. Any in vivo or in vitro identity relations were determined by linear regression (ideally, slope = 1 and intercept = 0), within a 95% confidence interval. Results: Phantom results demonstrated lower quantitative error for acquisitions using the 113-keV 177Lu energy peak rather than including the 208-keV peak, given that only low-energy collimation was available in this camera configuration. In the clinical study, 24 in vivo-in vitro pairs were eligible for further analysis, with 4 having been rejected as outliers (via Cook distance calculations). All linear regressions (R2 ≥ 0.82, P < 0.0001) provided identity in vivo-in vitro relations (95% confidence interval), with SUV averages from all users giving a slope of 0.96 ± 0.13, an intercept of -0.07 ± 0.46 g/mL, and an average residual difference of 19.5%. In acquisitions with the lower-energy 177Lu energy peak, solid-state SPECT/CT imaging provided an accuracy to within approximately 20% of in vivo urinary bladder radiotracer concentrations. Conclusion: This noninvasive in vivo quantitation method can potentially improve diagnosis, patient management, and treatment response assessment and provide data essential to 177Lu dosimetry.

Assessment of SPECT images using UHRFB and other low-energy collimators in brain study by Hoffman phantom and manufactured defects

The performance of collimators was investigated using low-energy high-resolution (LEHR) and low-energy ultra-high-resolution (LEUHR) collimators in SPECT system to study the brain physiology by injecting 99mTc-HMPAO radionuclide. Ultra-high-resolution fan beam (UHRFB) images were compared to other low-energy collimator images by constructed defects embedded into Hoffman brain phantom as lateral, deepness and metastasis designs with slices of Perspex. The defects were constructed by CNC machine as circular slices and ring flaws ranging in size from 2 to 16 mm to detect low-concentration regions. The data acquisition was done in tomographic mode with minimum radii and different matrix sizes, data acquisition time and number of projections. The collected data were reconstructed using two methods, filtered backprojection and ordered subset expectation maximization (OSEM). By two radiologists and via thallium and V-shaped markers, the minimum diameters of the constructed flaws inside the abnormal area of the brain phantom were diagnosed to 4.0 ± 0.4, 6.0 ± 0.7 and 8.0 ± 0.9 mm for UHRFB, LEUHR and LEHR, respectively. In OSEM method, the desirable ranges of the filter parameters were 4–8 iterations and 2–4 subsets for FB collimator. The outcomes showed that FB collimator provides the better resolution in axial, coronal and sagittal views using brain perfusion phantom and data from eight patients on tinnitus disease. The UHRFB with converging geometry confirmed the better detection of defect regions due to the lowest ratio of cold/background counts. This study may be useful for early detection of disease transference, monitoring of treatment response and disease progression. A CNC machine was used to make disks for Hoffman brain phantom as metastases and ring defects in evaluation of SPECT images.

Imaging cardiac sympathetic innervation with MIBG: linear conversion of the heart-to-mediastinum ratio between different collimators

BackgroundThe heart-to-mediastinum (H/M) ratio is a commonly used parameter to measure cardiac I-123 metaiodobenzylguanidine (MIBG) uptake. Since the H/M ratio is substantially influenced by the collimator type, we investigated whether an empirical linear conversion of H/M ratios between camera systems with low-energy (LE) and medium-energy (ME) collimator is possible.MethodsWe included 18 patients with parkinsonism who were referred to one of the two participating molecular imaging facilities for the evaluation of cardiac sympathetic innervation by MIBG scintigraphy. Two consecutive planar image datasets were acquired with LE and ME collimators at 4 h after MIBG administration. Linear regression analyses were performed to describe the association between the H/M ratios gained with both collimator settings, and the accuracy of a linear transfer of the H/M ratio between collimators and across centers was assessed using a leave-one-out procedure.ResultsH/M ratios acquired with LE and ME collimators showed a strong linear relationship both within each imaging facility (R2 = 0.99, p < 0.001 and R2 = 0.90, p < 0.001) and across centers (H/M-LE = 0.41 × H/M-ME + 0.63, R2 = 0.97, p < 0.001). A linear conversion of H/M ratios between collimators and across centers was estimated to be very accurate (mean absolute error 0.05 ± 0.04; mean relative absolute error 3.2 ± 2.6%).ConclusionsThe present study demonstrates that a simple linear conversion of H/M ratios acquired with different collimators is possible with high accuracy. This should greatly facilitate the exchange of normative data between settings and pooling of data from different institutions.

A new High-Resolution Imaging System (HiRIS2) detector for preclinical SPECT imaging

The aim of the work is to describe a new high-performance scintigraphic detector, derived from our previous work based on a Position Sensitive Photomultiplier Tube (PSPMT) with 256 output anodes. This detector is suitable for direct integration into multi-modality imaging systems. Indeed, the detector has been developed in order to be integrated into a pre-clinical system.The detector is based on an H9500 Hamamatsu PSPMT coupled to an LYSO pixelated scintillator and a low-energy tungsten collimator with parallel square holes. In order to limit the overall size of the device, a dedicated compact electronics has been developed. The device design was performed using Monte Carlo transport calculations to aid the development.Our results show a detector performance suitable for application on small animals. The intrinsic spatial resolution was experimentally determined to be about 1.6 mm. The measured energy resolution was ∼16% at 140 keV and the maximum recorded sensitivity was ∼76 cps/MBq. In addition, the results agree quite well with those of Monte Carlo simulations.We have successfully improved the performance of our previous detector design in order to integrate the new device into a complex system focused on pre-clinical imaging.

Effect of the LEGe detector collimators on K-series peaks and Compton scattering in XRF analysis using gamma rays

The effect of a low-energy germanium detector collimator with different diameters on the measurement of the X-ray fluorescence of palladium (Pd) was studied experimentally. Changes in the Pd K-series and Compton scattering peaks were measured and analysed with and without a detector collimator, where for the former, collimators with different diameters were used. The signal-to-noise ratio increased when a shielding collimator was used with a narrow detector collimator. The Compton dispersion and fraction dead time were reduced considerably using a detector collimator by increasing the distance from the source to the detector, and the collimator length-to-diameter ratio. The full width at half maximum (FWHM) of the Pd Kα1 and Pd Kβ1 peaks decreased almost linearly with the collimator length-to-diameter ratio. The FWHM illustrated that the spectral resolution was improved when a collimator with a smaller diameter but unchanged length was used. The uncertainties at the Pd Kα1, Pd Kβ1, and Compton dispersion peaks were approximately correlated linearly with the collimator length-to-diameter ratio.

OA108] Quantitative analysis of ventilation SPECT applied to krypton and technegas

Purpose Assessment of the state of the lungs by ventilation perfusion (V/Q) Single Photon Emission Computed Tomography combined with Computed Tomography (SPECT/CT) has proved its value as a clinical tool. Physicians study both ventilation and perfusion images, but also the ratio image of these two. However, the interpretation of these images is qualitative. For the ventilation images quantitative measures were investigated in the case of Krypton-81 m and Technegas (Tc-99 m labelled graphite particles). Krypton is a gaseous ventilation tracer and distributes similarly to air. However, it is not widely available and relatively expensive. Technegas is cheaper and has wider availability, but is an aerosol, which may result in hot spots in obstructed airways. Methods Dual-isotope ventilation SPECT/CT with both Technegas(140 keV) and Krypton(190 keV) simultaneously was obtained for 11 patients with medium and low energy general purpose collimators including a follow-up. This resulted in 38 ventilation studies in total. Reconstruction was performed with and without attenuation and scatter correction. The penetration index and the heterogeneity index (with and without band filtering for relevant clinical sizes) were calculated for the right and left lung. Scatterplots of the intensities of the Krypton and Technegas images were made and statistical outliers were detected. Results Significant lower penetration indexes for Technegas were found for the medium energy collimators, but were not seen for the low energy collimators. The higher heterogeneity indexes for Technegas were significant in all cases except for the uncorrected medium energy collimators data. Band filtering of the heterogeneity index improved the statistical significance of the differences. The scatterplots showed that all patients suffered from Technegas-outliers in one or both lungs, indicating the presence of hot spots. The visually identified hot spots could be mapped to the outliers seen in the scatterplots. Conclusions The applied quantitative analysis revealed that there are significant differences between Krypton and Technegas as a ventilation tracer for patients with severe COPD. The penetration index may have limited clinical relevance, since it does not capture complicated activity distributions. However, the heterogeneity index with band filtering is potentially a useful quantitative clinical measure.

Oligometastatic Prostate Cancer: Molecular Imaging and Clinical Management Implications in the Era of Precision Oncology.

1338 Objectives: Differentiated thyroid cancer (DTC) patients with elevated or rising serum thyroglobulin (Tg) levels and multiple other negative conventional imaging studies represent a clinically difficult group of patients. 99m Tc-sestamibi is a non-conventional imaging study for DTC that was used in the 1980s-1990s to help evaluate DTC patients before being replaced with 18F-FDG. However, 18F-FDG PET scans may also be negative in these patients. This is a preliminary analysis of our study to evaluate the diagnostic use of 99mTc-sestamibi scans to identify the source of elevated or rising Tgs in patients with negative conventional imaging including negative 18F-FDG PET scans. Methods This prospective study included DTC patients who were at least 18 years old, had at least one prior 131I therapy, and had elevated Tg>5 ng/ml or positive anti-Tg antibodies (TgAb). In addition, all of the following imaging studies must have been clinically reported as negative for recurrence or metastasis within the last 12 months: neck ultrasound, diagnostic radioiodine scan, chest x-ray, CT of the chest/abdomen with/without contrast, and 18F-FDG PET/CT. If other imaging studies were performed, such as bone scans or brain imaging, these must also have been read as negative. This study was approved by the IRB at MedStar Health and all participants signed informed consent. Participants were injected with 925 MBq (25 mCi) of 99mTc-sestamibi intravenously and whole body images were acquired after ~1h with acquisition speed 4cm/min with parallel-hole low-energy collimator. Extra spot view, pinhole view, or SPECT/CT images were performed when necessary. Two blinded nuclear medicine physicians independently interpreted the 99mTc-sestamibi images, and graded each foci 1-5 (1 = definite physiological uptake or artifact; 2 = most likely physiological uptake or artifact; 3 = indeterminate; 4 = most likely recurrence or metastasis; 5 = definite recurrence or metastasis). Discordant findings were resolved by consensus. Foci graded 3-5 were categorized as positive result and was followed-up for confirmation. Results A total of four patients completed the sestamibi scan to date. One out of four patients (Patient1) was positive on the sestamibi scan for distant metastasis. In Patient 1, the sestamibi whole-body posterior image demonstrated abnormal focal uptake in the right posterior calvarium and corresponding to an occipital lytic bone lesion on the SPECT/CT (Figure 1). The patient underwent surgical resection of the skull metastasis, and pathology confirmed metastatic thyroid cancer. Five months post-surgery the suppressed Tg was markedly reduced and stable at ~3.2ng/ml. Table 1 shows the sestamibi scan results, subsequent management and follow-up. With confirmation of the location of the metastatic foci in Patient 1, the two negative 18F-FDG PET/CT that were previously performed one year apart were reviewed again. The radiology reports did not document interpretation of the low-dose localization CT. In retrospect, the lytic skull metastasis was visible on both of the head CT, but could have been easily missed on the PET due to the normal intensive brain 18F-FDG activity. Conclusions In this preliminary analysis, 99mTc-sestamibi was able to identify the source of elevated Tg levels in one out of four DTC patients with biochemical recurrence and negative conventional imaging studies. 99mTc-sestamibi may have a role in thyroid cancer localization when physical exam, neck ultrasound, radioiodine scan, chest/abdomen CT, and 18F-FDG PET/CT could not identify. Additional patients are being recruited. Research Support We are grateful for the generous donations from our patients.

99mTc-DMSA renal cortical quantitative SPECT/CT imaging in diabetic patients: Feasibility and initial results

Introduction Diabetes mellitus is a common cause of chronic kidney disease. Radionuclide imaging of the kidneys using technetium-99m-labeled dimercaptosuccinic acid (99mTc-DMSA) is a well-established method for the evaluation of kidney parenchyma. We hypothesize that early preclinical detection of renal affection in diabetic patients can be done by quantitative single-photon emission computed tomography (SPECT) imaging using 99mTc-DMSA. Patients and methods In this study we included 29 patients: 13 diabetic and 16 volunteers as control. All must have within normal renal function. We excluded patients with known history of renal disease or abnormal renal function, patients with systemic diseases directly affect kidney function rather than diabetes. All patients included in our study were subjected to detailed clinical history, renal function, and quantitative 99mTc-DMSA renal imaging using SPECT/computed tomography techniques. About 5 mCi of 99mTc-DMSA were injected intravenously. Then imaging was acquired after 2–4 h in the supine position using a dual-head gamma camera with a low-energy all-purpose collimator. SPECT/computed tomography images are then taken. Data were reconstructed; then a 3D ball region of interest is drawn over each kidney to assess the counts of the kidney. Results There was a significant difference in the mean of the BMI-corrected counts divided by the injected dose (P = 0.024). The same results were obtained when the counts were summed and corrected according to the injected dose between the two groups (P = 0.034). Conclusion Quantitative SPECT 99mTc-DMSA imaging may have a role in the evaluation of renal functions in diabetics with no clinical evidence of renal affection.

A Comparison Between GATE and Accelerated Convolution-Based Forced Detection SIMIND for Low- and Medium-Energy Collimators: A Simulation Study

Monte Carlo is an important and well established research tool used in emission tomography. While used extensively in research applications, these techniques are not typically implemented clinically due to their low detection efficiency and long acquisition times. In order to make this computational tool faster, the variance reduction technique known as convolution-based forced detection (CFD) has been implemented into the SIMIND MC code (CFD-SIMIND) by our group. Briefly, at each site of interaction within the object, photons are forced to travel in a direction perpendicular to the detector and are then convolved with a distance dependent blurring kernel specific to that collimator and photon energy. A similar CFD method has already been implemented as an option in the SIMIND Monte Carlo program. This study performs a comparison between a well established, non-VRT Monte Carlo program, GATE, with our accelerated CFD-SIMIND. The intent of this work is to establish if CFD-SIMIND can either replace or be used in conjunction with GATE in order to gain significant reduction in simulation times for low and medium energy isotopes. A number of simulation studies were performed using point sources in air and water, along with the 3D XCAT phantom and a rectangular sheet source for 99mTc with low and medium energy collimator and 111In with medium energy collimator. A comparison in the projection domain was then performed in terms of spatial resolution, sensitivity, image profiles and energy spectra. The study has shown percent differences of between 3–5 % in sensitivity between CFD-SIMIND and GATE with mean universal image quality index value of 0.994 ± 0.009 and spatial resolution within 0.2 mm of each other. CFD-SIMIND offers a significant reduction in simulation time by a factor of 5–6 orders of magnitude compared to GATE. This acceleration time is useful for many applications. This study also provides an objective tool that can help to determine if CFD-SIMIND can be used in place of GATE in order to achieve images of sufficient quality within a reduced time and at much lower computational cost.

Characterization of "γ-Eye": a Low-Cost Benchtop Mouse-Sized Gamma Camera for Dynamic and Static Imaging Studies.

Several preclinical imaging systems are commercially available, but their purchase and maintenance costs make them unaffordable for the majority of small- and medium-sized groups. Taking into account the needs of average users, we developed "γ-eye", a mouse-sized, benchtop γ-camera suitable for in vivo scintigraphic imaging. The γ-eye is based on two position-sensitive photomultiplier tubes, coupled to a CsI(Na) pixelated scintillator and a low-energy lead collimator with parallel hexagonal holes. The spatial resolution of the system is 2mm at 0mm. The energy resolution is 26% at 140keV and the maximum recorded sensitivity 210 cps/MBq. The system was evaluated in a proof-of-concept animal study, using three different clinical Tc-99m-labeled radiopharmaceuticals. Phantom and animal studies demonstrate its ability to provide semiquantitative results even for short scans. Systems' performance, dimensions, and cost make γ-eye a unique solution for efficient whole-body mouse nuclear imaging.